Labour leader Jeremy Corbyn - who joined 200 Holocaust survivors at the service in Westminster - also shared a photo of himself signing the book, adding: "Let us never allow anti-Semitism or any other form of racism to disfigure our society."

Although Jews were the Nazis' main target, a wide range of other groups were persecuted during the Holocaust, including gay people, minority races, political opponents like communists and trade unionists, and Jehovah's Witnesses.

A quarter of a million mentally ill and disabled people and half a million Roma (also known as gypsies) were killed.

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A survivor at Auschwitz to mark International Holocaust Victims Remembrance Day on Sunday

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The memorial day coincides with the 74th anniversary of the liberation of Auschwitz, where people are laying wreaths

Holocaust survivor Steven Frank, who was one of 93 children to survive the Theresienstadt camp in Czechoslovakia along with his two brothers, said the survey's findings were "terribly worrying".

His father, who helped hide Jews as part of the Dutch resistance, was arrested in Amsterdam and gassed at Auschwitz, in Nazi-occupied Poland, in January 1943.

Mr Frank, who now lives in Hertfordshire, said he was "surprised" by the number of people who do not believe the Holocaust took place.

The 83-year-old said: "In my experience, people don't have a solid understanding of what happened during the Holocaust and that's one of the reasons I am so committed to sharing what happened to me.

"At one of my talks, I met someone who said the Holocaust didn't happen.

"The only way to fight this kind of denial and anti-Semitism is with the truth - I tell people what happened, what I saw and what I experienced."

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Steven Frank was one of 93 children to survive the Theresienstadt camp in Czechoslovakia

He added: "Education is so important. If we ignore the past, I fear history will repeat itself."